1. Field of the Invention
The present invention relates to a drive control circuit, in particular a drive control circuit for performing drive control of a plurality of loads. The present invention also relates to a projection apparatus equipped with such a drive control circuit.
2. Description of Related Art
A projection apparatus has an optical system made up of a lamp to be a light source, a polarizing beam splitter, a polarizing plate, a liquid crystal panel and the like, an it has a problem of heat generated from the optical system. Therefore, a usual projection apparatus has a fan for cooling the entire optical system by letting air in the apparatus flow, and a drive control circuit for performing drive control of the fan, in order to deal with the generated heat.
Recently, there is widespread a projection apparatus having a plurality of fans and a drive control circuit for performing drive control of the plurality of fans for a purpose of securing a sufficient cooling effect, improving the cooling effect or reducing a noise. FIG. 4 shows an example of a drive control circuit for performing drive control of a plurality of fans provided to a conventional projection apparatus.
FIG. 4 is a block diagram to show a general structure of the drive control circuit 900. The drive control circuit 900 includes a microcomputer 901, a first PWM conversion portion 902, a second PWM conversion portion 903, a first driver 904, a second driver 905, a first connector 906, a second connector 907, a first detecting portion 908 and a second detecting portion 909. Here, the first connector 906 is a connector for connecting to a first fan 910, while the second connector 907 is a connector for connecting to a second fan 911.
The microcomputer 901 is connected to the first PWM conversion portion 902 and the second PWM conversion portion 903. The first PWM conversion portion 902 is connected to the first driver 904, while the second PWM conversion portion 903 is connected to the second driver 905, respectively. The first driver 904 is connected to a plus terminal of the first connector 906, while the second driver 905 is connected to a plus terminal of the second connector 907, respectively. In addition, a minus terminal of the first connector 906 is connected to the first detecting portion 908, while a minus terminal of the second connector 907 is connected to the second detecting portion 909, respectively. Furthermore, the first detecting portion 908 and the second detecting portion 909 are connected to a terminal T91 of the microcomputer 901.
In the drive control circuit 900 having the structure described above, the microcomputer 901 delivers a control signal S1 to the first PWM conversion portion 902 for performing drive control of the first fan 910 and delivers a control signal S2 to the second PWM conversion portion 903 for performing drive control of the second fan 911. Furthermore, the first PWM conversion portion 902 performs PWM conversion on the control signal S1 and delivers an obtained signal to the first driver 904. In addition, the second PWM conversion portion 903 performs PWM conversion on the control signal S2 and delivers an obtained signal to the second driver 905.
The first driver 904 delivers a drive control signal to the first fan 910 via the plus terminal of the first connector 906 based on a signal from the first PWM conversion portion 902. In addition, the second driver 905 delivers a drive control signal to the second fan 911 via the plus terminal of the second connector 907 based on a signal from the second PWM conversion portion 903.
The first detecting portion 908 includes an operational amplifier 912 having a non inverting input terminal that is connected to a minus terminal of the first connector 906, an inverting input terminal to which a reference voltage is applied and an output terminal that is connected to the terminal T91 of the microcomputer 901, and a resistor R91 having one end that is connected to the minus terminal of the first connector 906 and the other end that is connected to the ground. In addition, the second detecting portion 909 includes an operational amplifier 913 having a no inverting input terminal that is connected to the minus terminal of the second connector 907, an inverting input terminal to which a reference voltage is applied and a output terminal that is connected to the terminal T91 of the microcomputer 901, and a resistor R92 having one end that is connected to the minus terminal of the second connector 907 and the other end that is connected to the ground.
In this case, if the first fan 910 is not connected to the first connector 906 or if the first driver 904 does not deliver the drive control signal to the first fan 910, no current flows in the minus terminal of the first connector 906. Therefore, the output terminal of the operational amplifier 912 delivers an L-level signal. In addition, if the first fan 910 is connected to first connector 906 and if the first driver 904 delivers the drive control signal to the first fan 910, current flows in the minus terminal of the first connector 906. Therefore, the output terminal of the operational amplifier 912 delivers an H-level signal.
In the same manner, if the second fan 911 is not connected to the second connector 907 or if the second driver 905 does not deliver the drive control signal to the second fan 911, current does not flow in the minus terminal of the second connector 907. Therefore, an L-level signal is delivered from the output terminal of the operational amplifier 913. In addition, if the second fan 911 is connected to the second connector 907 and if a drive control signal is delivered from the second driver 905 to the second fan 911, current flows in the minus terminal of the second connector 907. Therefore, an H-level signal is delivered from the output terminal of the operational amplifier 913.
For this reason, if the signal supplied to the terminal T91 is an L-level signal, the microcomputer 901 detects that the first fan 910 is not connected to the first connector 906, or that the drive control signal is delivered from the first driver 904 to the first fan 910, or that the second fan 911 is connected to the second connector 907, or that the drive control signal is delivered from the second driver 905 to the second fan 911.
In addition, if the signal supplied to the terminal T91 is an H-level signal, the microcomputer 901 detects that the first fan 910 is connected to the first connector 906, and that the drive control signal is delivered from the first driver 904 to the first fan 910, and that the second fan 911 is connected to the second connector 907, and that the drive control signal is delivered from the second driver 905 to the second fan 911.
In the drive control circuit 900 having the structure described above, the microcomputer 901 delivers the control signal S1 for performing drive control of the first fan 910 to the first PWM conversion portion 902, and it delivers the control signal S2 for performing drive control of the second fan 911 to the second PWM conversion portion 903. In this case, there is no problem if the first fan 910 and the second fan 911 has the same operating characteristic and the drive control method is the same between them. However, if the operating characteristic is different between the first fan 910 and the second fan 911, and if the drive control method is also different between them, it is impossible to perform drive control correctly for the first fan 910 and the second fan 911 in the case where the first fan 910 is connected to the second connector 907 and the second fan 911 is connected to the first connector 906, incorrectly.
Therefore, in the drive control circuit 900 the first connector 906 and the second connector 907 have different shapes so as to prevent the first fan 910 from being connected to the second connector 907 and prevent the second fan 911 from being connected to the first connector 906 incorrectly.
In addition, a control unit that can protect the incorrect connection is proposed (see JP-A-2005-076993), which is provided to an air conditioner using a power supply circuit that can delivers voltage generated by a voltage double rectifier from voltage after full wave rectification. It maintains the output voltage from the power supply circuit to be the voltage after the full wave rectification until it recognizes that an indoor unit and an outdoor unit have the same rated power voltage value, so as to protect components when incorrect connection is performed between units having different rated power voltage values.
However, when the drive control circuit 900 shown in FIG. 4 is manufactured, it is necessary to provide different manufacturing steps for the first connector 906 and the second connector 907 because the first connector 906 and the second connector 907 have different shapes. This may cause a problem of lowering production efficiency.
In addition, if the projection apparatus having the drive control circuit 900 shown in FIG. 4 is assembled manually, it is difficult to attach first one of the two connectors that is easier to attach since the first connector 906 and the second connector 907 have different shapes. This may also cause a problem of lowering production efficiency.
The control unit described in JP-A-2005-076993 can only detect incorrect connection due to a difference of the rated power voltage value. Therefore, even if this control unit is applied to the drive control circuit 900 shown in FIG. 4, it is necessary to arrange that the first connector 906 and the second connector 907 have different shapes. Further more, it is still difficult to attach first one of the two connectors that is easier to attach. Therefore, it is difficult to expect improvement of production efficiency.